1. Field of the Invention
The present invention relates to a capacitor charging circuit and, more particularly, to a circuit suitable for charging a capacitor.
2. Description of the Related Art
In a related flyback-type flash charging circuit, electric power supplied from a battery is boosted by a boosting transformer. Subsequently, a flyback pulse generated therein is rectified to thereby charge a main capacitor. When a picture is taken, the charged main capacitor is discharged to thereby cause a flash unit to flash. Japanese Patent Laid-Open No. 2002-6371 discloses an apparatus that controls charging of a main capacitor by disabling a clock signal to be inputted to a gate of an n-channel MOSFET (metal-oxide semiconductor field-effect transistor), which is connected in series to a primary winding of a boosting transformer, such that the n-channel MOSFET is maintained in an off-state during a second current flow through the boosting transformer.
However, the conventional charging circuit performs an oscillation operation based on PWM (Pulse Width Modulation) signals and needs PWM signals. Recent miniaturization of cameras has resulted in miniaturization of transformers. Thus, there is a limit to each of a primary inductance and a primary current, with the result of a high oscillating frequency. That is, the conventional charging circuit needs high-frequency PWM signals. Consequently, in some camera systems, the conventional charging circuit has a drawback in that a complex circuit for charging electric power in a capacitor is required.